Control unit and method for operating an industrial automation system communication network comprising a plurality of communication devices

ABSTRACT

Method for operating an industrial automation system communication network that includes a plurality of communication devices, and control unit, wherein at least one control unit controls functions of a plurality of assigned communication devices and is assigned to at least one partition of the communication network in order to operate an industrial automation system communication network comprising a plurality of communication devices, where partitions each include predefinable parts of communication devices assigned to system resources for predefinable resource periods of use, access periods and repetition cycles for transmit queues are set by the control unit according to the resource periods of use for the partitions in the assigned communication devices, where possible partitions are determined for the path reservation requests based on matching classifications of access periods and repetition cycles, and where the particular path reservation request is assigned to a determined partition when sufficient system resources exist.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application No. PCT/EP2016/082831 filedDec. 29, 2016.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to industrial automation systems and, moreparticularly, to a method for operating an industrial automation systemcommunication network comprising a plurality of communication devices,where at least one control unit controls functions of a plurality ofassigned communication devices

2. Description of the Related Art

Industrial automation systems are used for monitoring and open-loop andclosed-loop control of technical processes, in particular in the fieldof production automation, process automation and building automation,and allow control equipment, sensors, machines and industrial systems tobe operated in a manner that is meant to be, as far as possible,autonomous and independent of human interventions. The ever increasingrelevance of information technology to automation systems comprisingnumerous networked control units and processing units means that evengreater importance is attached to methods for reliably providingfunctions distributed over an automation system that are intended toprovide monitoring and open-loop and closed-loop control functions. Inindustrial automation systems, particular problems regularly result frommessage traffic containing messages that are relatively large in numberbut relatively short, thereby amplifying the problems above.

Software defined networking aims to virtualize communication networkfunctions by separating communication devices, such as routers orswitches, functionally into components assigned to a control plane and adata plane. The data plane comprises functions and/or components forforwarding data packets and/or data frames. The control plane, incontrast, comprises management functions for controlling the forwardingand/or the components of the data plane. OpenFlow, for example, definesa standard for software-implemented control planes. By abstractinghardware as virtual services, it is possible to dispense with manualconfiguration of the hardware, in particular by creating programmablecentral control of network traffic. OpenFlow supports partitioning ofsystem resources into network slices, which partitioning ensures thatdefined system resources are provided irrespective of other existingnetwork slices.

US 2013/268686 A1 discloses a method for sending a connectionestablishment request, where an OpenFlow switch sends a messagecontaining a parameter request to a configuration server to obtainconnection parameters from an OpenFlow controller. In response to themessage containing the parameter request, the OpenFlow switch receivesan IP address and a set of OpenFlow connection parameters from theconfiguration server, where the set of OpenFlow connection parameterscomprises at least connection parameters of a first OpenFlow controller.The OpenFlow switch sends a message containing a connectionestablishment request to the first OpenFlow controller according to theIP address and the set of OpenFlow connection parameters of the firstOpenFlow controller. It is thereby possible for a connection between anOpenFlow switch and an OpenFlow controller to be establishedautomatically.

WO 2013/110742 A1 relates to a control unit for providing communicationservices in a physical communication network. These communicationservices are used by a plurality of applications running oncommunication devices, with requirements made of the communicationservices specified for each of said applications. The control unitgenerates a communication network model, which represents a topology ofthe physical communication network and comprises a network node modelfor each communication device. The network node model describesfunctions and resources for the associated communication device. Inaddition, the control unit calculates, for each application running onthe communication devices, a virtual communication network by mappingonto the communication network model the requirements made by theparticular application of the communication services. The calculatedvirtual communication networks each comprise at least two network nodesdescribed by a network node model, and a partition or network slice ofselected communication network resources provided by the communicationdevices.

WO 2014/108178 A1 describes a method for connecting a booting switch toa communication network via a central control unit, which communicationnetwork comprises a multiplicity of where the controlled by the centralcontrol unit. In order to control the switches, the central control unittransmits data packets containing control information for the switchesvia the same communication paths as data packets containing user data.Each switch comprises a pipeline, in which are stored forwarding rulesfor data packets and which can be accessed via a local switch port. Thecommunication paths for the data packets containing control informationare established by storing forwarding rules defined by the centralcontrol unit in the pipelines of the switches. At least one of theswitches comprises a selected port, via which the booting switch isconnected to the communication network. In order for the central controlunit to store forwarding rules in the booting switch, a temporarycommunication path is used, which comprises a communication path betweenthe selected port and the central control unit, and a communication pathbetween the selected port and a local port of the booting switch. Thistemporary communication path allows access to the pipeline of thebooting switch.

WO 2015/096761 A1 describes data-traffic oriented dynamic zoning forsoftware defined networking (SDN), in which a network component receivescontrol information from an SDN controller of a plurality of SDNcontrollers. The network component determines available trafficengineering zones, and selects a local zone controller for eachdetermined traffic engineering zone. A master zone controller isselected based on the control information and a zoning scheme, where themaster zone controller and the local zone controllers are selected fromthe SDN controllers. In addition, the network component transmitsinformation about local zone controllers, zone membership and masterzone controllers to at least some of the SDN controllers.

For cycle-based control processes in industrial automation systems,where control commands must be transmitted regularly within apredetermined cycle time, the cycle time is used as the time base forperiodic data transmission. Owing to a typically rather small volume ofdata for control commands, the challenges that exist in industrialautomation systems lie less in providing sufficient bandwidth fortransmitting the control commands but, rather, in reliably guaranteeinga defined time window for transmitting these commands. Time-slice basedschedulers, for example, are used for this purpose, via which it ispossible to satisfy high requirements relating to latency and jitter. Aconsistent configuration of time-slice based schedulers is highlycomplex, however, in particular in industrial automation systems,especially because existing solutions for virtualization ofcommunication networks are aimed solely at bandwidth guarantees.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a simple andfailsafe method for configuring time-based access control for transmitqueues in industrial communication devices in the event of pathreservation requests, and to define a corresponding control unit forcommunication devices.

This and other objects and advantages are achieved in accordance withthe invention by having a control unit and method for operating anindustrial automation system communication network comprising aplurality of communication devices, where at least one control unitcontrols functions of a plurality of assigned communication devices.Said control unit is assigned to at least one partition of thecommunication network. Partitions comprise respectively specifiableportions of system resources of assigned communication devices forspecifiable resource utilization periods, and are preferably logicallydisjunct from one another. In addition, the communication devices eachcomprise at least one transceiver, where each transceiver is assigned aplurality of transmit queues, each of which is granted access to theassociated transceiver for a definable access time period within adefinable repetition cycle.

The communication devices can be assigned, for example, to a softwaredefined network, which comprises a communication control plane denotedas the control plane, and a data transmission plane denoted as the dataplane. Here, the control unit is assigned to the control plane, whereasthe communication devices are assigned to the data plane. In particular,the communication devices can comprise routers and/or switches, in whichcase the control unit can define flow tables, for example, from whichare derived routing and/or forwarding tables for communication devicesassigned to the control unit. The partitions are preferably networkslices, and are specified via an engineering system manually by a systemadministrator or in an automated manner.

In accordance with the invention, the access time periods and repetitioncycles for the transmit queues are set in the assigned communicationdevices by the control unit according to the resource utilizationperiods for the partitions. In addition, the partitions are classifiedaccording to the access time periods and repetition cycles set in theassigned communication devices. Path reservation requests for datastreams are classified correspondingly according to specified accesstime periods and repetition cycles. Potential partitions for the pathreservation requests are determined based on matching classifications ofaccess time periods and repetition cycles. The determined partitions arechecked to ascertain whether there are sufficient system resourcesavailable for the path reservation request concerned. If the result ofthe check is positive, then the path reservation request concerned isassigned to at least one determined partition, and system resourcesrequired for the path reservation request are reserved within thispartition. Simple and reliable configuration of communication networkpartitions is thereby possible, where the configuration can be adaptedflexibly to cycle times in an industrial automation system. It is alsopossible to rule out any mutual influence between the partitions.

In accordance with an advantageous embodiment of the method inaccordance with the invention, the control unit determines communicationnetwork paths for each of the path reservation requests, taking intoaccount system resources available in the relevant partition, andcontrols routing or switching functions of the communication devicesaccording to the determined communication network paths. The controlunit preferably determines the communication network paths based on aquality measure. Path costs, for example, can be applied as the qualitymeasure for determining the communication network paths by the controlunit.

The control unit can set the transmit queues of the communicationdevices for data streams having different repetition cycles bydetermining for the different repetition cycles a smallest commonmultiple as the total repetition cycle. Here, the different repetitioncycles for the transmit queues are embedded in the total repetitioncycle at a frequency equal to a quotient of the total repetition cycleand the particular repetition cycle. The access time periods for therespective transmit queues are preferably identical, while the differentrepetition cycles are each an integer multiple of a fundamental cycle.

In theory, during commissioning of the communication network, the systemresources can be assigned to a plurality of control units such that theyare partitioned in an equally distributed manner. The partitions arethen modified by the control units according to a given resourceutilization and/or resource requirement. During commissioning of thecommunication network, the system resources are preferably partitionedaccording to known and/or estimated classifications of communicationrequirements on the part of automation devices to be connected to thecommunication network. Matching classifications of access time periodsand repetition cycles can thereby be expected in the event of pathreservation requests. Thus path reservation requests can be acceptedwithout the need to modify partitions.

Control units can each be assigned, for example, to at least one tenant,one user and/or one application. In addition, the path reservationrequests can each be initiated by a tenant, a user and/or anapplication. The access time periods and repetition cycles for thetransmit queues of the communication devices are preferably controlledvia Time Aware Shaper as defined in Institute of Electrical andElectronic Engineering (IEEE) standard 802.1Qbv.

The control unit in accordance with the invention is intended to performa method in accordance with the above statements, and is configured tocontrol functions of a plurality of assigned communication devices, andto be assigned to at least one partition of a communication network. Thepartitions each comprise specifiable portions of system resources ofassigned communication devices for specifiable resource utilizationperiods. In addition, the control unit is configured to set in theassigned communication devices, access time periods and repetitioncycles for transmit queues according to the resource utilization periodsfor the partitions. The communication devices also each comprise atleast one transceiver. Each transceiver is assigned a plurality oftransmit queues, each of which is granted access to the associatedtransceiver for a definable access time period within a definablerepetition cycle.

In accordance with the invention, the control unit is configured toclassify the partitions according to the access time periods andrepetition cycles set in the assigned communication devices, and toclassify path reservation requests for data streams according tospecified access time periods and repetition cycles. Furthermore, thecontrol unit is configured to determine potential partitions for thepath reservation requests based on matching classifications of accesstime periods and repetition cycles, and to check the determinedpartitions to ascertain whether there are sufficient system resourcesavailable for the path reservation request concerned. In addition, thecontrol unit is configured to assign the path reservation requestconcerned, if the result of the check is positive, to at least onedetermined partition, and to reserve within this partition, systemresources required for the path reservation request.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in greater detail below from anexemplary embodiment with reference to the drawing, in which:

FIG. 1 shows an industrial automation system communication networkcomprising a plurality of communication devices and control unitsassigned to these devices in accordance with the invention;

FIG. 2 shows a flow diagram for reserving system resources by thecontrol units of the communication system shown in FIG. 1;

FIG. 3 shows a schematic diagram of granting data streams havingdifferent repetition cycles, access to transmit queues of thecommunication devices shown in FIG. 1.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The communication network shown in FIG. 1 of an industrial automationsystem comprises a plurality of communication devices 200 and aplurality of the control units 101, 102. For example, the communicationdevices 200 may be switches, routers or firewalls, and may be used forconnecting programmable logic controllers 300 or input/output units ofthe industrial automation system. Programmable logic controllers 300typically each comprise a communication module, a central processingunit and at least one input/output unit (I/O module), and hence likewiseconstitute communication devices. In principle, input/output units canalso be formed as distributed I/O modules, which are arranged remotelyfrom a programmable logic controller.

A programmable logic controller 300 is connected, for example, to aswitch or router or additionally to a fieldbus via the communicationmodule. The input/output unit is used for transferring controlquantities and measured quantities between the programmable logiccontroller 300 and a machine or apparatus 400 controlled by theprogrammable logic controller 300. The central processing unit isprovided in particular for determining suitable control quantities fromacquired measured values. The aforementioned components of theprogrammable logic controller 300 are connected to one another via abackplane system in the present exemplary embodiment.

In the present exemplary embodiment, the communication devices 200 areassigned to a software defined network (SDN), which comprises acommunication control plane 1 denoted as the control plane, and a datatransmission plane 2 denoted as the data plane. The control units 101,102 as SDN controllers are assigned to the control plane, whereas thecommunication devices are assigned to the data plane. The control units101, 102 define, for example, flow tables for switches or routers, fromwhich are derived routing tables and/or forwarding tables forcommunication devices 200 assigned to the respective control units 101,102.

In the present exemplary embodiment, the control units 101, 102 are eachassigned to at least one tenant, in particular to a user or to anapplication. The control units 101, 102 are generally configured tocontrol functions of a plurality of assigned communication devices 200,and are each assigned to a partition of the communication network. Inthe present exemplary embodiment, the partitions are network slices, andcan be specified via an engineering system manually by a systemadministrator or in an automated manner. In particular, the networkslices comprise respectively specifiable portions of system resources ofassigned communication devices 200 for specifiable resource utilizationperiods, where the network slices are preferably logically disjunct fromone another. A separate resource view 111, 121 of the portions of systemresources that are assigned to the corresponding network slice ispreferably provided for each control unit 101, 102.

System resources include, for example, port bandwidth, queue buffers,DHCP address ranges, VLAN identifiers and routing-table entries orforwarding-table entries. In theory, during commissioning of thecommunication network, the system resources can be assigned to thecontrol units 101, 102 such that they are initially partitioned in anequally distributed manner. The network slices can then be modified bythe control units 101, 102 according to a given resource utilizationand/or resource requirement. During commissioning of the communicationnetwork, the system resources are preferably partitioned according toknown and/or estimated classifications of communication requirements onthe part the automation devices to be connected to the communicationnetwork.

The communication devices 200 comprise at least one transceiver or oneport each, where each transceiver or port is assigned a plurality oftransmit queues. Each of the transmit queues is granted access to theassociated transceiver or the associated port for a definable accesstime period within a definable repetition cycle. The access time periodsand repetition cycles for the transmit queues are set in the assignedcommunication devices 200 by the control units 101, 102 according to theresource utilization periods for the network slices. The access timeperiods and repetition cycles for the transmit queues of thecommunication devices 200 can be controlled, for example, by means ofTime Aware Shaper as defined in IEE 802.1Qbv.

In step 201 of the flow diagram shown in FIG. 2 for reserving systemresources, the network slices are classified according to the accesstime periods and repetition cycles set in the assigned communicationdevices. This can be performed, for example, by an engineering system aspart of project planning. In addition, the control units 101, 102continually monitor, in accordance with step 202, whether pathreservation requests exist from tenants, users and/or applications.Existing path reservation requests for data streams are classified (step203) according to access time periods and repetition cycles specified inthe path reservation request concerned. In accordance with step 204, thecontrol units 101, 102 determine based on matching classifications ofaccess time periods and repetition cycles, for the path reservationrequests potential network slices within which a path reservation ispossible in principle. If there are no matching classifications, theparticular path reservation request is rejected, in accordance with step210. Data streams assigned to rejected path reservation requests can betransmitted, in principle, as best effort data in free timeslots,without maintaining quality guarantees. In addition, it is also possibleto reserve specific timeslots for best effort data.

In the case of there being matching classifications, the control units101, 102 determine, in accordance with step 205, communication networkpaths for each of the path reservation requests, taking into accountsystem resources available in the particular network slice. For example,the control units 101, 102 determine the communication network pathsbased on path costs. In addition, the control units 101, 102 areconfigured to check, in accordance with step 206, the determined networkslices to ascertain whether there are sufficient system resourcesavailable for the particular path reservation request. If sufficientsystem resources are not available, the particular path reservationrequest is rejected, in accordance with step 210. Notification of therejection can comprise, for example, suggestions for a new reservationrequest using modified parameters.

If sufficient system resources are available, then the particular pathreservation request is assigned, in accordance with step 207, to adetermined network slice, and system resources required for the pathreservation request are reserved within this network slice (step 208).On this basis, the control units 101, 102 control, in accordance withstep 209, routing or switching functions of the communication devicesaccording to the determined communication network paths.

Within a technical process, data streams often have the same repetitioncycle. In the case of superimposed or hierarchical closed-loop controlsystems, however, different repetition cycles can arise that differsignificantly from one another. Different repetition cycles make itharder to configure a time-based scheduler for Time Aware Shaper,however. Configuring the scheduler includes specifying all the times atwhich a gate for a transmit queue is opened or closed. When a gate isopen, data can be transmitted out of the transmit queue assigned to thegate concerned. Data from a transmit queue that has a closed gate cannotbe transmitted, however.

The control units 101, 102 set the transmit queues of the communicationdevices 200 for data streams having different repetition cycles bydetermining for the different repetition cycles a smallest commonmultiple as the total repetition cycle. Here, the different repetitioncycles for the transmit queues are embedded in the total repetitioncycle at a frequency equal to a quotient of the total repetition cycleand the particular repetition cycle.

FIG. 3 shows two scenarios, each having two data streams 311-312,321-322 and different repetition cycles, while the access time periodequals 5 ms in each case. According to a first scenario, a first datastream 311 has a repetition cycle of 10 ms, whereas a second data stream312 has a repetition cycle of 33 ms. A large total repetition cycle of330 ms not only results in fundamentally poor bandwidth utilization butalso creates a problem because gate reservations for the first datastream 311 and for the second data stream 312 would be in conflict fromtimeslot 41 to timeslot 43 (timeslot length 1 ms in each case) in thefirst scenario.

As a result, the different repetition cycles are adjusted in a secondscenario such that they are each an integer multiple of a fundamentalcycle. Although a first data stream 321 again has a repetition cycle of10 ms in the second scenario, a repetition cycle of 30 ms is selectedfor a second data stream 322. Thus, in the second scenario, the totalrepetition cycle 323 can be shortened to 30 ms, and conflicting gatereservations can be avoided. Thus, in the case of different repetitioncycles, an adjustment should always be made in accordance with thesecond scenario.

Thus, while there have been shown, described and pointed out fundamentalnovel features of the invention as applied to a preferred embodimentthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices illustrated, and intheir operation, may be made by those skilled in the art withoutdeparting from the spirit of the invention. For example, it is expresslyintended that all combinations of those elements and/or method stepswhich perform substantially the same function in substantially the sameway to achieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements shownand/or described in connection with any disclosed form or embodiment ofthe invention may be incorporated in any other disclosed or described orsuggested form or embodiment as a general matter of design choice. It isthe intention, therefore, to be limited only as indicated by the scopeof the claims appended hereto.

The invention claimed is:
 1. A method for operating an industrialautomation system communication network comprising a plurality ofcommunication devices, at least one control unit controlling functionsof a plurality of assigned communication devices and being assigned toat least one partition of the communication network, partitions of thecommunication network comprising respectively specifiable portions ofsystem resources of assigned communication devices for specifiableresource utilization periods, the communication devices each comprisingat least one transceiver which is assigned a plurality of transmitqueues, each of which is granted access to the associated transceiverfor a definable access time period within a definable repetition cycle,and the access time periods and repetition cycles for the transmitqueues being set in the assigned communication devices by the controlunit according to the resource utilization periods for the partitions,the method comprising: classifiying the partitions according to theaccess time periods and repetition cycles set in the assignedcommunication devices; classifying path reservation requests for datastreams according to specified access time periods and repetitioncycles; determining potential partitions for the path reservationrequests based on matching classifications of access time periods andrepetition cycles; checking the determined partitions to ascertainwhether sufficient system resources are available for a relevant pathreservation request; and assigning the relevant path reservation requestto at least one determined partition, and reserving system resourcesrequired for the relevant path reservation request within the determinedpartition when sufficient system resources are available for therelevant path reservation request.
 2. The method as claimed in claim 1,wherein the control unit determines communication network paths for eachof the path reservation requests, taking into account system resourcesavailable in the relevant partition, and controls routing or switchingfunctions of the communication devices according to the determinedcommunication network paths.
 3. The method as claimed in claim 2,wherein the control unit determines the communication network pathsbased on a quality measure.
 4. The method as claimed in claim 3, whereinpath costs are applied by the control unit as the quality measure fordetermining the communication network paths.
 5. The method as claimed inclaim 1, wherein the control unit sets the transmit queues of thecommunication devices for data streams having different repetitioncycles by determining for different repetition cycles a smallest commonmultiple as the total repetition cycle; wherein the different repetitioncycles for the transmit queues are embedded in the total repetitioncycle at a frequency equal to a quotient of the total repetition cycleand a particular repetition cycle; and wherein the access time periodsfor the respective transmit queues are identical, and the differentrepetition cycles are each an integer multiple of a fundamental cycle.6. The method as claimed in claim 1, wherein the communication devicesare assigned to a software defined network which comprises acommunication control plane denoted as the control plane and a datatransmission plane denoted as the data plane; wherein the control unitis assigned to the control plane; and wherein the communication devicesare assigned to the data plane.
 7. The method as claimed in claim 6,wherein the partitions are network slices which are specified via anengineering system manually by a system administrator or specified in anautomated manner.
 8. The method as claimed in claim 7, wherein duringcommissioning of the communication network, the system resources areassigned to a plurality of control units such that said system resourcesare partitioned in an equally distributed manner; and wherein thepartitions are subsequently modified by the control units according toat least one of (i) a specific resource utilization and (ii) a resourcerequirement.
 9. The method as claimed in either claim 7, wherein duringcommissioning of the communication network, the system resources arepartitioned according to at least one of (i) known and (ii) estimatedclassifications of communication requirements with respect to automationdevices to be connected to the communication network.
 10. The method asclaimed in claim 7, wherein the network slices are logically disjunctfrom one another.
 11. The method as claimed in claim 6, wherein duringcommissioning of the communication network, the system resources areassigned to a plurality of control units such that said system resourcesare partitioned in an equally distributed manner; and wherein thepartitions are subsequently modified by the control units according toat least one of (i) a specific resource utilization and (ii) a resourcerequirement.
 12. The method as claimed in either claim 6, wherein duringcommissioning of the communication network, the system resources arepartitioned according to at least one of (i) known and (ii) estimatedclassifications of communication requirements with respect to automationdevices to be connected to the communication network.
 13. The method asclaimed in claim 6, wherein the communication devices comprise at leastone of (i) routers and (ii) switches, and wherein the control unitdefines flow tables, from which at least one of (ii) routing tables and(ii) forwarding tables for communication devices assigned to the controlunit are derived.
 14. The method as claimed in claim 1, wherein at leastone of (A) control units are each assigned to at least one of (i) atleast one tenant, (ii) one user and (iii) one application and (B)wherein the path reservation requests are each initiated by a at leastone of (i) tenant, (ii) a user and (iii) an application.
 15. The methodas claimed in claim 1, wherein the access time periods and repetitioncycles for the transmit queues of the communication devices arecontrolled via Time Aware Shaper as defined in Institute of Electricaland Electronics Engineers (IEEE) standard 802.1Qbv.
 16. A control unitcomprising: a processor; and memory; the control unit being configuredto: control functions of a plurality of assigned communication devices,and to be assigned to at least one partition of a communication network,partitions of the communication network each comprising specifiableportions of system resources of assigned communication devices forspecifiable resource utilization periods, set in the assignedcommunication devices, access time periods and repetition cycles fortransmit queues according to the resource utilization periods for thepartitions, said communication devices each comprising at least onetransceiver, and each transceiver being assigned a plurality of transmitqueues, each of which is granted access to the associated transceiverfor a definable access time period within a definable repetition cycle,classify the partitions according to the access time periods andrepetition cycles set in the assigned communication devices, classifypath reservation requests for data streams according to specified accesstime periods and repetition cycles, determine potential partitions forthe path reservation requests based on matching classifications ofaccess time periods and repetition cycles, check the determinedpartitions to ascertain whether sufficient system resources areavailable for a relevant path reservation request, assign the relevantpath reservation request concerned to at least one determined partitionand, reserve within this partition, system resources required for thepath reservation request when sufficient system resources are availablefor the relevant path reservation request.